The finishing of a wide variety of articles of manufacture is often accomplished by the application, i.e. by spraying, dipping or brushing, of one or more coatings of paint. The term "paint" as used herein is intended to refer to any of the wide variety of colored or clear protective, sealant or decorative compositions based on natural or synthetic film-forming compositions. Paints commonly used for metallic surfaces include enamels, lacquers and latexes based on phenolic, polyester, alkyd, acrylic, polyurethane and polyepoxide resins.
Paint removal in finishing operations is important for two reasons. First, the periodic treatment of support devices such as paint hooks, jigs and hangers, as well as paint booth components to remove accumulated paint residue is necessary for their continuous day-to-day use. Secondly, efficient paint removal is necessary to avoid the need to scrap defectively-painted parts and to increase the ease of recycling scrapped painted metal articles.
Aqueous alkaline paint strippers commonly employed to remove paint from metal surfaces can be aqueous solutions of a wide variety of organic and inorganic compounds. The alkalinity is primarily provided by an alkali metal hydroxide. Other ingredients include buffers, corrosion inhibitors, surfactants, detergents and chelating agents. Typically, paint strippers include active ingredients at a total concentration of about 5-50% by weight of the total composition, e.g. one-half to several pounds per gallon, and are used at about 50.degree.-115.degree. C. The painted articles to be stripped are exposed to these stripping solutions by a dipping, spraying or other coating procedure, and following an adequate exposure period, the loosened paint film and adhered stripper are typically removed by a water rinse.
Alkali metal salt-based paint removers often employ water-miscible organic additives or accelerators to enhance the ability of the stripping composition both to penetrate the paint film and to dissolve or suspend the loosened paint. Common stripping bath accelerators include phenolic compounds such as cresylic acid and primary, secondary or tertiary monoamines of the general formula R.sub.1 R.sub.2 R.sub.3 N wherein 1-3 of R.sub.1, R.sub.2 and R.sub.3 are (lower)alkanol; hydroxy-, aryloxy- or alkoxy-substituted ethers; lower(alkyl) or aryl. These amines may also be used in combination with alkylene glycols or glycol ethers. For example, U.S. Pat. Nos. 3,615,825 and 3,972,839 disclose paint-stripping compositions prepared by combining low molecular weight hydroxyalkyl- or alkoxyalkyl amines with alkaline solutions, while U.S. Pat. Nos. 3,671,465 and 3,663,447 disclose alkaline stripping compositions incorporating mixtures of tripropylene glycol or an alkylene glycol monophenyl ether with hydroxyalkyl- or alkoxyalkyl-monoamines.
However, a continuing demand for improved accelerators exists due to the suspected carcinogenicity of phenolics and the tendency of many of the lower molecular weight alkanolamines, alkoxylated primary amines and aromatic amines to thermally decompose and volatilize during the stripping process, producing noxious ammonia-like vapors and reducing the useful life of the stripping bath.
Clearly, a substantial need exists for paint stripping baths comprising accelerators which are effective when used alone or in combination with known accelerators, which are relatively nonvolatile, and which are stable when combined with aqueous alkaline solutions.